Superalloys are group VIIIA (Co, Fe, Ni) metal base alloys with large and varied amounts of alloying elements. Superalloys currently dominate high-temperature service applications, such as jet engines, up to the 1038.degree.-1093.degree. C. (1900-2000 F.) range. Although superalloys are pushing the limits of their capabilities with little appreciable gain in operating temperature expected, the demand for still higher operating temperatures [1093.degree.-1370.degree. C. (2000-2500 F.) ] remains strong. What is therefore needed is a new alloy system based on a metal with a higher melting point than the superalloy base metals, nickel (1453.degree. C.), cobalt (1495.degree. C. ) and iron (1535.degree. C.). Niobium, with a melting point of 2468.degree. C., appears to be one such material. Wadsworth and Froes [1989] reviewed the state-of-the-art for metallic materials and concluded that a major problem was the inherent lack of oxidation resistance of niobium alloys at high temperature. Hix, in U.S. Pat. No. 2,822,268, teaches the improvement of oxidation resistance in niobium alloys through the addition of titanium, aluminum, beryllium, carbon, cobalt, iron, manganese, molybdenum, nickel, silicon, tantalum, tungsten, vanadium, and zirconium in combined amounts of everything except titanium from one to twenty percent by weight. Rhodin, in U.S. Pat. No. 2,838,395, teaches the use of one to twenty five weight percent iron in conjunction with one to twenty percent aluminum in niobium alloys containing at least fifty five percent niobium to improve oxidation resistance. Rhodin, in U.S. Pat. No. 2,838,396, teaches the use of one to thirty weight percent chromium in conjunction with one to twenty percent aluminum in niobium alloys containing at least fifty five percent niobium to improve oxidation resistance. Thielemann, in U.S. Pat. No. 2,860,970, teaches the use of niobium alloys containing three to twenty percent chromium, two to eight percent aluminum, and three to ten percent vanadium for improved oxidation resistance. Rhodin, in U.S. Pat. No. 2,881,069, teaches the addition of five to twenty weight percent aluminum and in excess of five percent and up to twenty percent molybdenum to produce oxidation resistance. Rhodin, in U.S. Pat. No. 2,882,146, teaches the use of titanium, molybdenum, chromium, tantalum, vanadium, zirconium, aluminum, cobalt, iron, manganese, nickel, tungsten, beryllium, carbon, cerium, and silicon to produce oxidation resistance. Wainer, in U.S. Pat. No. 2,883,282, teaches the addition of rare earths including cerium, erbium, lanthanum, neodymium, praseodymium, together with at least one element selected from the group consisting of beryllium, titanium, aluminum, zirconium, chromium, silicon, and vanadium. Thielemann, in U.S. Pat. No. 2,907,654, teaches the use of tantalum, chromium, and tungsten to develop oxidation resistance in niobium alloys. Semmel, in U.S. Pat. No. 3,156,560, teaches the use of scandium, yttrium, and rare earth elements of the lanthanide series to develop alloys which are ductile at elevated temperatures. Bradley, Rausch, McAndrew, and Simcoe, in U.S. Pat. No. 3,168,380, teach the use of aluminum and silicon in specific atomic ratios with niobium to develop high temperature oxidation resistance. Jaffee, Williams, Bartlett, and Bradley, in U.S. Pat. No. 3,193,385, teach the addition of tantalum, tungsten, molybdenum, hafnium, zirconium, vanadium, chromium, and beryllium to develop superior strength qualities. Begley, Buckman, and Ammon, in U.S. Pat. No. 3,206,305, teach the use of tantalum, vanadium, zirconium, and hafnium, to develop high strength at elevated temperatures in niobium alloys. Anna, in U.S. Pat. No. 3,346,380, teaches the addition of tungsten and rhenium to niobium to develop ductility in niobium alloys as well as useful strength at elevated temperatures. None of these inventions teaches, however, the addition of gold to niobium or niobium alloys to develop oxidation resistance or mechanical properties.
None of this prior art teaches the addition of gold to niobium-containing alloys or to other high-temperature turbine engine alloys. These alloys are all invariably crystalline or polycrystalline. We have now discovered that gold additions to these alloys, both those that contain niobium as well as those that do not contain significant amounts of niobium, confer substantial beneficial improvements in the properties of these alloys. Such alloys can be expected to have application in turbine engines and turbine engine environments within a temperature range of 500.degree.-1500.degree. C. The following preferred embodiments demonstrate the scope and range of these improvements.